This invention relates to vibrating screens used, e.g., for separating rock into different sizes and more particularly to the manner of lubricating the gears utilized for producing the desired vibrations.
Vibrating flat screens receive material to be screened (an admixture of differently sized rock) at one end of the top deck of screen or screen-cloth and the material is moved toward the opposite end by vibration. In the process, rocks of a size that fit through the screen openings are dropped through those openings and likely onto a second deck having somewhat smaller sized screen openings where the process is repeated. There may be a third screen deck and however many decks are used, the larger sized rock (larger than the screen-cloth openings) are forced off the end of each deck and collected (the bottom most deck will deposit its screened material, e.g., gravel, onto an underlying conveyor or chute to also be collected).
The vibration of the screen is angularly directed from the receiving end to the opposite end (collection end) and is achieved by mounting the assembly of screens on springs. Gears mounted to the screen assembly are provided with weights mounted off center. Due to centrifugal force, the circular motion of the weights will tend to lift up and then push down on the spring supports. As the action is very rapid, the screens are effectively vibrated. The angular direction of the vibrating motion is achieved by placing a weight on each of a plurality of gears with at least one gear being rotated in the opposite direction to the other or others. By arranging the weights on the respective gears so that they become aligned at, e.g., the 10:00 and 4:00 positions, the vibration will be directed angularly from the receiving end to the collecting end (right to left as illustrated in the drawings).
These gears become heated and it is necessary to maintain the heat below a specified temperature. To facilitate cooling, the gears are lubricated. This is accomplished by placing the gears in a closed box and partially filling the box with a low viscosity lubricant, e.g., oil, but only to a level just below the bottom of the gears. The box is vibrated with the screen assembly which produces oil spikes that project up onto the gears and more importantly into the path of the rotating weights mounted on the gears. The oil spikes are contacted by the weights and thrown or flung upwardly onto the entirety of the gears.
The above application of lubrication to the gears allows more rapid vibration. However, the upper limit of vibration (above which the maximum temperature is exceeded) is still below that which is sometimes desired. It is accordingly an objective of the present invention to modify the prior design and enable a higher rate of vibration (via higher rotation of the gears) without exceeding the temperature limit.
The present invention is derived from an investigation of what effects temperature rise in the oil bath. It was surmised that the weight attached to the gears impact the oil spikes and the impact itself generates heat. The weights are typically segments of a thick ring of steel, each ring being cut into three segments and each segment comprising a weight to be attached to a gear. The ends of the segments are a flat face that is positioned radial to the gear axis. Thus, a flat face having the dimension of the weight (width and height, e.g., 3xe2x80x3xc3x975xe2x80x3) is rapidly rotated into the oil spikes and results in a hammer-like splattering of the oil that induces heating.
The invention eliminates this hammer-like impact with a configuration that engages the oil with a sweeping action. The weight more closely resembles a crescent shape which is beneficial in providing a leading face that is a curved edge rather than a flat face that impacts the oil. This leading edge wipes or sweeps through the oil spikes and carries and throws a portion of the oil as the weight is rotated around the gear axis. It is more accurately described as a sweeping or wiping and throwing action as differentiated from the impacting action of the prior system.
With the modifications to the configuration of the weights as described, tests have established that the gears can indeed be accelerated to higher rotative speeds, achieving the benefits of the accelerated vibration, but without exceeding the established temperature maximum and without losing the lubrication benefits.
A further benefit is achieved by producing the weights from multiple thin plates rather than a single thick plate. First, the crescent shape can be cut from a rectangular plate with the crescent shapes cut out of the plates in a nested relationship. Waste material is significantly reduced. Second, the several weight segments making up a weight can be varied in length and arranged in a shingled relation so that the weight has a compound curve as its leading face.
A further benefit of the invention as may be surmised is that the impact action of the prior weights produces a splattering action which causes the oil to settle into pockets between the weights. This is undesirable and significantly reduced with the present invention. The above benefits and others will become apparent to those skilled in the art and will be more fully appreciated upon reference to the following detailed description having reference to the accompanying drawings.